A data transmission cable for connection to mobile devices includes at least two insulated conductors twisted into a pair, in which the pair is enclosed by an electric shield over which a jacket of insulating material is applied.
Such data transmission cables—hereinafter referred to as “cables” for short—are intended for use as flexible cables for connecting mobile devices with a voltage or signal source. Such devices can be, for example, cranes, machine tools and robots. The cables must withstand high mechanical loads and their bending and torsional strength must remain constant over an indefinite period of time. They must also remain flexible over a wide range of temperatures, for example −40° to +80° C. The elements of these cables must further be constructed in such a way that the transmission of data at increased data rates is not affected. This applies, in particular, to data rates greater than 100 Mbit/sec. In addition to the lowest possible attenuation of the data to be transmitted, adequate electric shielding is also required so that external fields do not influence the data transmission and so that a cable of this type does not emit interfering radiation.
In conventional, commercially available cables, the conductors are insulated with a foamed material so as to obtain the lowest possible dielectric constant. Although this is useful electrically, it has a negative effect on the mechanical and thus also the electrical properties of such a cable. The foamed insulation materials with wall thicknesses ranging around 0.2 mm are relatively soft and can easily be compressed if subjected to frequently alternating bending and torsional stresses. The cables are further shielded by a copper wire braid, which as a rule has sufficient electric density at higher frequencies or data rates to prevent passive or active interference with the cables. Such a shield is not suitable, however, for cables in robotic applications. It is easily destroyed by the frequently alternating bending and torsional stresses.